Guan Zhiping

The analysis of the bending stiffness and intensity of cylindrical tubes

Based on the mechanics of material, the bending stiffness and intensity of cylindrical bar and tube are analyzed. By comparing the cylindrical tube whose ratio of outside diameter to internal diameter is 0.7 with the cylindrical bar, it is concluded that when both of them have the same mass, the section stiffness of the cylindrical tube is three times that of the cylindrical bar; when both of them have the same external diameter, the mass of the cylindrical tube is only 1/2 that of the cylindrical bar, but the section stiffness of the cylindrical tube is 3/4 that of the cylindrical bar. By virtue of the elemental elastic-plastic theory, the yield stress of the liquid-filled cylindrical tube is investigated. Due to the incompressibility of liquid and the strain hardening effect of material, the yield stress of the liquid-filled tube is enlarged compared with the hollow tube, thus raising its bending intensity. Under the dynamic load, compared with the hollow tube, the impact resistance of the liquid-filled tube is also raised due to elastic recovery. Because the hydraulic pressures perpendicular to the inner surface are identical everywhere, the local stress concentration resulting from the ovalisation of the tube would be decreased, and the resistance to buckling would be improved.

Theoretical and metrical standardization of strain rate sensitivity index

AbstractStrain rate sensitivity index m is one of the vital mechanical parameters for determining material superplasticity. In this paper, the existing formulae for measuring m value are reviewed, and it is found that the m values can be classified into three classes: mi under constant length, mv under constant velocity, and mp under constant load. The constraint equation of the generalized m value is established according to the tensile constitutive equation and the basis theory for plastic mechanics. Based on three typical deformation paths, the m value is redefined. Furthermore, from the formula of generalized m value, the formulae for measuring mi, mv and mp are theoretically deduced. The precise methods with numerical simulation are presented. The results prove that the m value is a non-constant and its dependence on

Mechanical analysis of superlastic bulge in a cylindrical die

\dot \varepsilon

Mechanical analysis of temperature impact on stability during superplastic tensile deformation

changes with the deformation path. Under different deformation paths, the m values calculated from the same formula are different. Using different formulae, the m values under the same deformation path are also different. Therefore, deformation path and corresponding formula should be given during the measurement of the m value. Moreover, it is explained theoretically and experimentally that why the mv value under constant velocity is sometimes negative but the mp value under constant load is sometimes lager than 1. The aim of the analysis and measurement of the m value is to facilitate the study on the relationship between macroscopical mechanical laws and microscopic physical mechanisms during superplastic deformation.

THEORETICAL AND EXPERIMENTAL STANDARDIZATION OF STRAIN HARDENING INDEX IN TENSILE DEFORMATION

The matter of fracture in tension is also the issue of fracture elongation. The ability of superplasticity of materials is mainly characterized by excellent fracture elongations. Since first su- perplastic phenomenon was recorded, the investigations of superplasticity have not halted. Most of the existing literatures focused on physical or microstructural mechanisms while less attention was paid to mechanical theories on the superplastic deformation. However, superplastic phenomena on large elon- gation in superplastic tension are closely related to the mechanical stability and are finally dependent on the special fracture mechanism. Correspondingly, in this article, the studies of fracture mechanism of the superplastic deformation are reviewed, which involved nucleation, growth and coalescence of cavities. Then, the literatures related to the mechanical stability in superplastic tension are classified and reviewed, which involved the mechanical analysis and numerical simulation of the fracture elonga- tion or the limit strain induced from necks initiation and development. The conclusions indicate that there has yet been no united and confirmed opinion on the superplastic fracture mechanism which has numerous versions from the microstructural or physical view, and the superplastic fracture mechanism would have maken no significant progress unless many long-term investigations will be carried out in the future. In order to interpret the essence of large fracture elongation, the current task should be thoroughly investigate the mechanical stability in superplastic tension based on the advanced technol- ogy of numeric analysis. In numeric analysis, the precise and quantitative constitutive equation should be adopted and the deformation conditons involving strain paths should be taken into account.

Lever type fixed load material testing machine

Previous mechanical analytical theories of superlastic bluge into a shaped die are all based on uniform thinning assumption, but in fact, the thinning process is obviously non-uniform. In this paper, the non-uniform thinning mechanical analytical equations of superlastic bluge in a cylindrical die based on superlastic bulge constitutive equation with variable m are established and verified by experiments performed on typical superlastic material ZnAl4Cu alloy sheet. Experimental results show that non-uniform thinning mechanical analytical model can reflect the deformation process of bulging in a cylindrical die. Supported by National Natural Science Foundation of China (Grant No. 50075035)

Testing device and testing method for forming limit diagram under high-temperature constant-strain rate condition

Take Yunma-2 as the research object discussed the shearing force and shearing strength of the bottom stalk of china-hemp. The study showed that the mean maximum shearing force was 1373.8N; the mean maximum shearing strength was 10.87 MPa in harvesting period. The maximum shearing force increased along with the stalk diameter, and the shearing characteristics were influenced mostly by the stalks maturity, moisture content and so on, the results showed that shearing strength increased with the decrease of the stalk moisture content. Passing through the regression analysis and the testing of notable nature, the empirical formula of the harvest stalk diameter and the maximum shearing force could be defined. The regression equation significance was specified. The results provided the design basis for the manufacture of China-hemp harvesting machinery.

Forming limit diagram's testing arrangement under permanent rate of strain condition of high temperature

Based on state equation that stress is the function of strain, strain-rate and temperature, the paper establishes the differential constitutive equation used for analyzing load-stability and the variational constitutive equation used for analyzing geometry-stability during superplastic tensile deformation, which contain strain hardening index, strain-rate sensitivity index, temperature sensitivity index introducted for the first time and temperature undulation index introducted for the first time in the paper. And then, based on the universal condition of plastic elementary theory, the paper analyzes load-stability and geometry-stability under continuously rising temperature and under the non-uniform temperature along the axes of specimen respectively. The results prove the impact of continuously rising speed and non-uniform value of temperature on deformation stability is that the faster temperature rises and the more non-uniform temperature is, the smaller the corresponding uniform strain of load-stability and geometry-stability are; strain hardening index is the necessary condition of stability during superplastic tensile deformation, and geometry-instability will not happen when load-instability occurs, but happen when uniform deformation has lasted after load-instability; in the superplastic temperature field, constant temperature is not necessary condition of superplasticity, but during the deformation, the slower temperature rises and the more uniform temperature is, the more stable deformation is.